Pain
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Habituation and sensitization to heat and cold pain in women with fibromyalgia and healthy controls.
The purpose of this study was to examine differences in habituation to heat and cold pain in women with fibromyalgia (FM; n=33) and in women who were healthy controls (HC; n=44). Quantitative sensory testing (QST) was used to assess pain thresholds during five consecutive trials of ascending heat and descending cold stimulation. Anxiety, depression, fatigue, and pain during the previous week were assessed using self-report measures. ⋯ In addition, anxiety, depression, fatigue, and pain were related to decreased heat and cold pain thresholds in the overall sample. However, when group was controlled, none of these variables were related to thresholds or rates of habituation or sensitization. The differences between women with FM and healthy women in habituation and sensitization may have important implications for the etiology, diagnosis, and treatment of FM and other chronic pain conditions.
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In chronic musculoskeletal pain conditions, the balance between supraspinal facilitation and inhibition of pain shifts towards an overall decrease in inhibition. Application of a tonic painful stimulus results in activation of diffuse noxious inhibitory controls (DNIC). The aims of the present experimental human study were (1) to compare DNIC, evoked separately, by hypertonic saline (6%)-induced muscle pain (tibialis anterior) or cold pressor pain; (2) to investigate DNIC evoked by concomitant experimental muscle pain and cold pressor pain, and (3) to analyze for gender differences. ⋯ When cold pressor and muscle pain were applied concomitantly the PPT increases were smaller when compared to the individual sessions. This study showed for the first time that two concurrent conditioning tonic pain stimuli (muscle pain and cold pressor pain) cause less DNIC compared with either of the conditioning stimuli given alone; and males showed greater DNIC than females. This may explain why patients with chronic musculoskeletal pain have impaired DNIC.
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Provoked vestibulodynia (PVD) is a common form of chronic vulvar pain with unknown aetiology. Central pain regulatory mechanisms have been suggested to be disrupted in PVD, and consequently, PVD may be associated with anatomical changes in pain modulatory brain areas. Here, we compared total gray matter volumes and regional gray matter densities between 14 medication-free young women with relatively short-standing PVD (1 to 9 yrs) and 14 control subjects using whole brain voxel-based morphometry (VBM). ⋯ These results point at the morphological alterations in supra-spinal pain modulatory circuitry, which might contribute to the clinical symptoms of patients with PVD. Previous VBM studies in older subjects with a longstanding chronic pain condition have demonstrated gray matter decreases in similar areas. We therefore speculate that gray matter density might increase in young pain patients with short disease duration and decrease in older subjects with longstanding disease, similarly to some psychiatric conditions, in which bi-directional changes of gray matter have been observed.
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A few experimental observations have suggested that diffuse noxious inhibitory control (DNIC)-type inhibition acts preferentially on the pain system if this is in a sensitised state, e.g. after slow temporal summation (wind-up). However, firm evidence is still missing. Furthermore, sex-related factors, which seem to affect temporal summation as well as DNIC effects, might thus also modulate the interaction of these two processes. ⋯ Sex differences were not observed for temporal summation, DNIC inhibition or for the interaction of the two processes, although women exhibited significantly lower pressure pain thresholds and higher ratings for the tonic heat stimuli. In conclusion, DNIC-type inhibition apparently does not preferentially act on a sensitised pain system after slow temporal summation. Considering the sex of the subjects does not change this insight.
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Osteoarthritis (OA) is a major healthcare burden of increasing prevalence. It has been demonstrated that the relationship between pain and sleep produces changes in sleep patterns and pain perception. However, electrophysiological studies in animal models of pain are limited. ⋯ These changes in sleep pattern occurred mostly between days 10 and 28. In the dark period, sleep disturbances were also characterized by decreased sleep efficiency, slow-wave sleep, and paradoxical sleep, although sleep was only initially fragmented. Thus, pain associated with the rat OA model causes alterations in sleep architecture by disrupting the sleep pattern.